Improved allograft survival, occasionally leading to a state of stable transplant tolerance in immunologically mature mammalian systems is achievable by a variety of methods, usually including the use of antilymphocyte antibody preparations and some form of donor cell infusion. Models vary with respect to type of allograft and the timing/route of drug and donor cell administration but many combinations have proved successful. Despite these advances, the clinical application of many of these methods is hampered by the lack of consistent and reliable results in higher primates and man, along with the realities of technical, logistical and chronological limitations inherent in human transplantation. There is, therefore, further need to examine options in the transfusion associated induction of improved allograft survival in solid organ transplantation.
Certain factors have not been fully addressed. First, the avoidance of intensive immunosuppression to limit the incidence of opportunistic infection and tumor formation makes a protocol that avoids use of potent antibody preparations desirable. Second, the enrichment of an antigen/cell source allowing sufficient supply for the multiple recipients of organs from a single cadaveric donor is important. Lastly, the application of an in vitro culture method to enrich immunomodulatory cells could allow for the use of important cytokines and other agents not easily tolerated in-vivo.
The use of either donor blood, bone marrow cells or splenocytes has proved most successful in the induction of prolonged graft survival. In some of these models, the generation of a suppressor-type cell appears to be operative. In other work, the generation of potent suppressor cell populations has been achieved by in-vitro culture of bone marrow with the use of stimulators, especially lipopolysaccharide (LPS). The administration of granulocyte macrophage-colony stimulating factor (GM-CSF) or granulocyte colony stimulating factor ("G-CSF") to donors of bone marrow DST enhances allograft survival. Furthermore, GM-CSF is known to activate marrow-derived natural suppressor cell function. The fractionation of both cell cultures and transplant cellular sources can isolate and enrich subpopulations of cells that retain the properties of suppressor cell function and equally prolong allograft survival.
Transplantation
A major goal in solid organ transplantation is the permanent engraftment of the donor organ without a graft rejection immune response generated by the recipient, while preserving the immunocompetence of the recipient against other foreign antigens. Typically, in order to prevent host rejection responses, nonspecific immunosuppressive agents such as cyclosporine, methotrexate, steroids and FK506 are used. These agents must be administered on a daily basis and if stopped, graft rejection usually results. However, a major problem in using nonspecific immunosuppressive agents is that they function by suppressing all aspects of the immune response, thereby greatly increasing a recipient's susceptibility to infections and other diseases, including cancer.
Furthermore, despite the use of immunosuppressive agents, graft rejection still remains a major source of morbidity and mortality in human organ transplantation. Most human transplants fail within 10 years without permanent graft acceptance. Only 50% of heart transplants survive five years and 20% of cadaveric kidney transplants survive 10 years. (See Opelz et al., 1981, Lancet 1:1223; Gjertson, 1992, UCLA Tissue Typing Laboratory, p. 225; Powles, 1980, Lancet, p. 327; Ramsay, 1982, New Engl. J. Med., p. 392). It would therefore be a major advance if tolerance to the donor cells can be induced in the recipient.
The only known clinical condition in which complete systemic donor-specific transplantation tolerance occurs is when chimerism is created through bone marrow transplantation. (See Qin et al., 1989, J Exp Med. 169:779; Sykes et al., 1988, Immunol. Today 9:23; Sharabi et al., 1989, J. Exp. Med. 169:493). This has been achieved in neonatal and adult animal models as well as in humans by total lymphoid irradiation of a recipient followed by bone marrow transplantation with donor cells. The success rate of allogeneic bone marrow transplantation is, in large part, dependent on the ability to closely match the major histocompatibility complex ("MHC") of the donor cells with that of the recipient cells to minimize the antigenic differences between the donor and the recipient, thereby reducing the frequency of host-versus-graft responses and graft-versus-host disease ("GVHD"). In fact, MHC matching is essential, only a one or two antigen mismatch is acceptable because GVHD is very severe in cases of greater disparities. In addition, it also requires the appropriate conditioning of the recipient by potential lethal doses of total body irradiation (TBI) or cytotoxic drugs.
The MHC is a gene complex that encodes a large array of individually unique glycoproteins expressed on the surface of both donor and host cells that are the major targets of transplantation rejection immune responses. In the human, the glycoproteins are referred to as HLA (human leukocyte antigen) antigens. When HLA identity is achieved by matching a patient with a family member such as a sibling, the probability of a successful outcome is relatively high, although GVHD is still not completely eliminated. However, when allogeneic bone marrow transplantation is performed between two MHC-mismatched individuals of the same species, common complications involve failure of engraftment, poor immunocompetence and a high incidence of GVHD. Unfortunately, only about 20% of all potential candidates for bone marrow transplantation have a suitable family member match.
The field of bone marrow transplantation was developed originally to treat bone marrow-derived cancers. It is believed by those skilled in the art even today that lethal conditioning of a human recipient is required to achieve successful engraftment of donor bone marrow cells in the recipient. In fact, prior to the present invention, current conventional bone marrow transplantation has exclusively relied upon lethal conditioning approaches to achieve donor bone marrow engraftment. The requirement for lethal irradiation of the host which renders it totally immunocompetent poses a significant limitation to the potential clinical application of bone marrow transplantation to a variety of disease conditions, including solid organ or cellular transplantation, sickle cell anemia, thalassemia and aplastic anemia.
Immunosuppressive agents are also extensively used following organ transplantation for the prevention of rejection episodes. In particular, cyclosporine, a potent immunosuppressive agent, prolongs the survival of allogeneic transplants involving skin, heart, kidney, pancreas, bone marrow, small intestine, and lung in animals. Cyclosporine has been demonstrated to suppress some humoral immunity and to a greater extent, cell mediated reactions such as allograft rejection, delayed hypersensitivity, experimental allergic encephalomyelitis, Freund's adjuvant arthritis, and graft versus host disease in many animal species for a variety of organs.
U.S. Pat. No. 5,514,364, Ildstad, issued May 7, 1996, discloses non-lethal methods of conditioning a recipient for bone marrow transplantation. In particular, it relates to the use of sub-lethal doses of total body irradiation, cell type-specific antibodies, especially antibodies directed to bone marrow stromal cell markers, cytotoxic drugs, or a combination thereof. The methods of the invention have a wide range of applications, including, but not limited to, the conditioning of an individual for hematopoietic reconstitution by bone marrow transplantation for the treatment of hematological malignancies, hematological disorders, auto immunity, infectious diseases such as acquired immunodeficiency syndrome, and the engraftment of bone marrow cells to induce tolerance for solid organ, tissue and cellular transplantation.
U.S. Pat. No. 5,486,359, Caplan et al., issued Jan. 23, 1996, discloses isolated human mesenchymal stem cells which can differentiate into more than one tissue type (e.g., bone, cartilage, muscle or marrow stroma), a method for isolating, purifying, and culturally expanding human mesenchymal stem cells (i.e., "mesenchymal stem cells" or "hMSCs"), and characterization of and uses, particularly research reagent, diagnostic and therapeutic uses for such cells. The stem cells can be culture expanded without differentiating.
None of these references individually or collectively teach or suggest the present invention.